Hey folks, I thought about buying some IC based output protection relays, similar IC's are used in some older commercial amplifier output protection. What do you think, are they good , have anyone had any experience with these?
https://www.ebay.com/itm/264663559721?hash=item3d9f2d6e29:g:cV0AAOSwIGhgQFrY
https://www.ebay.com/itm/3040842555...h4gQMExbZixuMb0Vly1at2/Ihw==|tkp:BFBMnM260blf
They seem very simple , basically all I need is DC protection in case of amplifier fault and overload or short circuit protection.
https://www.ebay.com/itm/264663559721?hash=item3d9f2d6e29:g:cV0AAOSwIGhgQFrY
https://www.ebay.com/itm/3040842555...h4gQMExbZixuMb0Vly1at2/Ihw==|tkp:BFBMnM260blf
They seem very simple , basically all I need is DC protection in case of amplifier fault and overload or short circuit protection.
The first one is only rated at 5amps @ 30vdc, the second one is rated at 10amps @ 30vdc.
The problem with relays is the possibility of the contacts welding closed whilst trying to break the circuit under a short circuit condition.
Here are a couple of solid state versions which offer the same protection (plus you get support via the forum):
https://www.diyaudio.com/community/threads/speaker-protection-board.377896/
https://www.diyaudio.com/community/threads/rtr-ssr-speaker-protection-gb-4.378742/
The problem with relays is the possibility of the contacts welding closed whilst trying to break the circuit under a short circuit condition.
Here are a couple of solid state versions which offer the same protection (plus you get support via the forum):
https://www.diyaudio.com/community/threads/speaker-protection-board.377896/
https://www.diyaudio.com/community/threads/rtr-ssr-speaker-protection-gb-4.378742/
I've used the unit in the second link in a couple of amplifiers and thought it was well made. Of course I can't be sure that all of the components are really what they are labelled. It is true relays deteriorate over time and use, but relays have been used for speaker protection by the gazillions so I am inclined to think that the relay in the first link is suitably rated for a 100+ watt amplifier if it is in-fact an Omron. The current rating is the life cycle switchable capacity, not the maximum current that can be conducted while the contacts are closed. It is good practice to not switch on or off an amplifier when the volume is near maximum. If you follow that practice the relay is not going to weld the first time an over-current opening occurs.
The first link for the UPC1237 based SSR board seems very interesting , possibly I am thinking of DIY that board, thanks for sharing.
As for the second board I don't understand which are the devices used for actual switching of the output, I only see SMD devices I wonder what is the maximum current rating for that board.
I agree I think ordinary relays if of good quality work well enough for most practial applications, they have been used for countless even top brand amplifiers like Onkyo or Lyxman etc, but given this is a DIY site and a pair of mosfets and some resistors are cheap I could as well go the extra mile and make my own small board using a SSR protection like the one in the link. Given ebay takes a month of not more to send from China I would also be faster in making my own little board.
Here is an example from a diyaudio member when their protection relay contacts fused together and took out a bass driver in their B&W 703 when the amplifier output transistors failed short circuit - Output Relays
Omron general purpose relays like those used for speaker protection typically have a DC current switching rating at 125V that is equal to the AC switching rating at 250V, so there should be no risk of welded contacts if an appropriate relay is used.
Paralleling relays is not as straight forward as is seems. Because the relays will not have identical switch times, inevitably one relay which switch the entire 'on' current, and one relay (not necessarily the same one) will switch the entire 'off' current. The benefit in parallel relays is the 'on' resistance once all of the contacts have closed. For fault protection it would be better to choose a single relay with an appropriate rating for the task.
One wonders in the example above why the power supply protection failed, or perhaps wasn't present! The power supply should have shut down, e.g. fuses blow, long before the speaker drivers were damaged, unless the amplifier was grossly over-specified for the connected speaker system.
Paralleling relays is not as straight forward as is seems. Because the relays will not have identical switch times, inevitably one relay which switch the entire 'on' current, and one relay (not necessarily the same one) will switch the entire 'off' current. The benefit in parallel relays is the 'on' resistance once all of the contacts have closed. For fault protection it would be better to choose a single relay with an appropriate rating for the task.
One wonders in the example above why the power supply protection failed, or perhaps wasn't present! The power supply should have shut down, e.g. fuses blow, long before the speaker drivers were damaged, unless the amplifier was grossly over-specified for the connected speaker system.
Probably more to do with trying to break the circuit under a inductive load rather than a purely resistive one. The datasheets have different ratings for each type of load.
Not exactly one of those boards, but I have been using Ebay's UPC+Omron board for 5+ years. So far, no issue.
Well one thing is certain, mosfets used as SSR in a protection board work much faster than mechanical relays. If a relay has adequate current rating for DC used it will work I'm sure and if one only uses a bass driver with a thick coil the speaker might survive a fault condition for some limited time but if one uses a speaker cabinet with multiple speakers , midrange and tweeters a fault condition even for a short time can cause damage not to the bass driver but to the tweeter for example. So in this regard a mosfet based output relay would be better much like a GFCI breaker will be faster than a regular amperage rated breaker which is the reason GFCI are used in applications that are sensitive to the time and amount of overcurrent like saving a human life from a shock in a bathroom.
I need speaker startup and shutdown protection for my Crown DC300 power amp, capable of handling these specs:
150Wpc into 8 ohms (21.8dBW) per channel, 250Wpc into 4 ohms (21dBW) per channel, Frequency response: DC–20kHz.
https://www.stereophile.com/content/crown-dc-300-power-amplifier-specifications
Much appreciation if you can point me towards the most reliable solution asap that I can purchase and put into use now. I don't have time to study the subject, but need to implement asap.
Many thanks,
Nick
150Wpc into 8 ohms (21.8dBW) per channel, 250Wpc into 4 ohms (21dBW) per channel, Frequency response: DC–20kHz.
https://www.stereophile.com/content/crown-dc-300-power-amplifier-specifications
Much appreciation if you can point me towards the most reliable solution asap that I can purchase and put into use now. I don't have time to study the subject, but need to implement asap.
Many thanks,
Nick